2D ultrasonic transducer array for two dimensional and three dimensional imaging

ABSTRACT

An ultrasonic 2D array has elements extending in two dimensions which can be individually controlled and operated to form a 2D array for scanning a volumetric region in three dimensions. Individual ones of the elements can also be selected and operated together to form a 1D array for scanning a planar region in two dimensions. An ultrasonic probe containing the inventive array can be quickly switched between two and three dimensional imaging modes to produce both a three dimensional image and a two dimensional image in real time.

This invention relates to transducer arrays for ultrasonic diagnosticimaging systems and, in particular, to a two dimensional array which canbe selectively operated for either two dimensional imaging or threedimensional imaging.

Both one dimensional (1D) and two dimensional (2D) transducer arrays arein use today for ultrasonic imaging. A 1D array consists of a flat rowof transducer elements. A 1D array may be configured as a straight lineof transducer elements or as a curved row of elements in the azimuthdirection, which is the in-plane direction orthogonal to the beamdirections which extend in the plane of the image in the rangedirection. The single row of elements may be controlled by selectivelyapplying pulses at predetermined times to the individual elements totransmit a beam of ultrasonic energy which can be steered and focused inazimuth. The array can receive echoes from along the same beamdirection. A single row of elements is confined to transmitting andreceiving in a planar region in front of the emitting surface of thearray. The 1D array has a fixed focus in the elevation dimensionorthogonal to the image plane, which may be provided by an acousticallens, curvature of the transducer, or both. This fixed elevational focusdetermines the thickness of the slice represented by the two dimensionalimage.

A 2D array is an array of transducer elements which extends in twodimensions, sometimes referred to as the azimuth and elevationdirections, where the elevation direction is transverse to the azimuthdirection. The 2D array is controlled in the same manner as the 1Darray, by pulsing individual elements at selected times to transmitbeams which can be steered and focused in both azimuth and elevation. 2Darrays can be either annular (composed of ring-shaped elements) orrectilinear (composed of rows and columns or other patterns ofindividual elements). Annular arrays formed of continuous rings can befocused in both azimuth and elevation but can only be directed straightahead. Rectilinear 2D arrays can be focused and steered in bothdimensions and hence can be used to steer beams through a threedimensional volumetric regions for three dimensional imaging.

Other, more restricted, variation of the 2D array are known, referred toas 1.5D and 1.75D arrays. A 1.5D array generally has fewer elements inthe elevation direction than in the azimuth direction, and has pairs ofelements symmetrically located on either side of a central row ofelements. This enables the 1.5D array to be dynamically focused in theelevation direction, but the symmetrical operation of the elements oneither side of the center row prohibits any elevational steering. A1.75D array can be electronically steered in both azimuth and elevation,but only to a minimal extent as compared to a 2D array. Compared to 1Darrays, both 1.5D and 1.75D arrays are used to control slice thicknessthrough dynamic elevation focusing.

Generally, 1D transducer arrays are optimized for use in two dimensionalscanning while 2D transducer arrays are optimized for use in threedimensional scanning. Two dimensional slices of a three dimensionalimage can be displayed with lower image quality than a two dimensionalimage obtained from a 1D array. When a user wants to switch between twodimensional imaging and three dimensional imaging, the user must usuallychange transducer probes. It would be desirable to have a singletransducer probe which could be used for both two dimensional and threedimensional imaging and which performs with the image quality of a 1Dprobe when used for two dimensional imaging.

In accordance with the principles of the present invention, a 2Dtransducer array is provided which can be used for three dimensionalimaging and is switchable to operate as a 1D array for two dimensionalimaging. Connections between elements of the 2D array are switched,preferably in the probe itself, so that echo signals are combined priorto being processed by the system beamformer. In an illustratedembodiment the 2D array can be operated with fully populated 1Dapertures for two dimensional imaging or with sparsely populated 2Dapertures for three dimensional imaging. A transducer probe of thepresent invention can advantageously be used to periodically acquire atwo dimensional image frame using the fully-populated 1D aperture duringthe acquisition of a three dimensional volume of data by the sparse 2Daperture.

IN THE DRAWINGS

FIG. 1 is a plan view of a 2D array transducer constructed in accordancewith the principles of the present invention;

FIG. 1a illustrates the transducer elements of the embodiment of FIG. 1which are not used when the transducer is operated as a sparse 2D array;

FIG. 2 illustrates a first switching configuration used to switch thearray transducer of FIG. 1 between a sparse 2D array and afully-populated 1D array;

FIG. 3 illustrates a second switching configuration used to switch thearray transducer of FIG. 1 between a sparse 2D array and afully-populated 1D array;

FIG. 4 illustrates a second embodiment of the present invention whichutilizes different transmit and receive apertures for 3D imaging;

FIG. 5 illustrates the 2D sparse receive aperture of the embodiment ofFIG. 4;

FIG. 6 illustrates a fully populated transmit aperture of the embodimentof FIG. 4;

FIG. 7 illustrates the embodiment of FIG. 4 when configured as a 1Darray; and

FIGS. 8a and 8 b illustrate the assembly of a transducer probeconstructed in accordance with the principles of the present invention;

FIG. 9 illustrates in block diagram form an ultrasound system includinga transducer probe of the present invention;

FIGS. 10a, 10 b, and 10 c illustrate a transducer probe of the presentinvention which is switchable to form two orthogonal 1D arrays;

FIG. 11 illustrates the scanning of a three dimensional volume, a planarregion, and a quantified spectral display in a time interleaved manner;and

FIG. 12 illustrates the scanning of a three dimensional volume and twoplanar regions within that volume.

Referring first to FIG. 1, a 2D array transducer constructed inaccordance with the principles of the present invention is shown in aplan view. Each square in this drawing represents one transducer elementin a two dimensional array of elements containing nineteen rows andnineteen columns of elements, a total of 361 elements. If this arraywere to be operated as a conventional 2D array, it would require 361signal leads, one connected to each transducer element. A 19×19 array isshown for ease of illustration, however an actual constructed embodimentmay be sized as a 60×60 element array or greater. Such a constructedembodiment would require 3600 signal leads. When it is considered thateach signal lead is a coaxial wire, it is seen that a cable for aconstructed embodiment can be inconveniently large in diameter andcostly.

In the drawing of FIG. 1 alternate ones of the elements are darklyshaded. These are the elements used in this embodiment when the 2D arrayis to be operated as a sparse 2D array. A “sparse” array is one in whichthere are inactive spaces in the array aperture between the activetransducer elements. In operation the active elements of the sparse 2Darray 10 are individually operated to transmit and receive steered andfocused ultrasound beams in the three dimensional region in front of the2D array aperture. In this embodiment the unshaded array elements 14 arenot used when the darkened elements 12 operate as a sparse 2D array.While sparse arrays have unfavorable implications for some imagingparameters such as sensitivity and grating lobes, sparse array operationcan result in favorable trade-offs for other characteristics such asresolution, beamformer channel requirements, cost, frame rate, andpractical cable size. The illustrated sparse 2D array has one hundredactive elements 12, requiring only one hundred signal conductors in thecable, a substantial reduction from the 361 conductors required for fullpopulation of the aperture. The unused elements 14 can be leftelectrically open, can be connected together, can be grounded, or can beconducted to ground potential by an impedance to control the electricalboundary conditions on the elements that are not used in the sparse 2Darray.

In an embodiment of the present invention transducer elements which arenot used (not active) in the sparse 2D array aperture can be connectedfor use as active aperture elements when the 2D array is to be operatedas a 1D array. These elements are shown in FIG. 1a for the 2D array ofFIG. 1. The elements in each column 16, 17, 18, 19, etc. are connectedtogether electrically at the acoustic stack, in the backingblock/interconnect structure, or at another point in the electricalinterconnect path. In the illustrated example of FIG. 1a, the 261elements that are not used in the sparse 2D array configuration areconnected to form a 1D array with 19 elements, one element per column.Only nineteen electrical connections for signal leads are needed toaccess the 1D array, one for each 1D element. No additional fabricationsteps are required. The only additional complexity in array fabricationis to provide the means for connecting elements together in columns.Some examples of ways to do this are described below.

The resulting 1D array has holes in the locations corresponding to theelements in the sparse 2D array, and every other 1D element of the array(e.g., 16 and 18) has half as much active area as those 1D elements madeup of a complete column (e.g., 17 and 19). This nonuniformity andsparseness of the 1D array can be eliminated by adding to each alternatecolumn 16, 18, etc. the elements that comprise the sparse 2D array.

The cable required to support such an array can have threeconfigurations. First, additional coaxes can be added to the cable, oneper column, and have the beamformer in the ultrasound system sum thesignals from all of the elements in each column. In this example, thecable has 119 coaxes, 100 for the active elements of the sparse 2D array(FIG. 1) and nineteen for the nineteen 1D array elements (FIG. 1a).

A second alternative, which also has 119 coaxes, uses a high-voltagemultiplexer with 200 switches to include the sparse 2D array elements intheir 1D array columns, so that all of the 1D elements have the sameactive area. Each element in the sparse 2D array requires two switches:one to connect the element to the 2D array coax, and one to connect itto the 1D coax. Such a switching configuration is shown in FIG. 2 fortwo array columns, column 26 which includes alternate elements 12 of thesparse 2D array aperture and column 27 which is an entire column ofelements not used in the sparse 2D array configuration but used as aunitary 1D array element (e.g., columns 17 and 19 in FIG. 1a). Forsparse 2D array operation, switches 2D0-2D9 connect the darkly shadedtransducer elements 12 of the first column 26 to coax cables C0-C9. Noneof the elements 14 of the second column 27 are used in the sparse 2Darray configuration; they are all connected together and go to coaxcable C11 for use during 1D array operation. Those (unshaded) elementsin the first column 26 which are not used in the sparse 2D arrayconfiguration are connected together, and connect directly to cable C10.In addition, the sparse 2D elements in the first column are connected tocable C10 through switches 1D0-1D9. The switch pairs 1D0/2D0 through1D9/2D9 are operated as single-pole double-throw switches. When the 2Darray is to be operated as a sparse 2D array, switches 2D0-2D9 areclosed, switches 1D0-1D9 are left open and coax cables C0-C9 and thelike coaxes of the other columns are used to access the shaded arrayelements 12. Coaxes C10, C11 and the like conductors are grounded, leftfloating, or connected to an impedance as desired. For 1D operationswitches 2D0-2D9 are opened, switches 1D0-1D9 closed, and coaxes C10,C11 and the like conductors of the cable are used to access the elementsof each array column as a single element of a 1D array.

It will be noted that the connections of coax C10 to the unshadedelements in column 26 and of coax C11 to the unshaded elements in column27 illustrate the connections necessary to form the partially sparse 1Darray configuration of FIG. 1a.

A third implementation is to switch the 1D array onto the coaxes used bythe sparse 2D array, so that no additional coaxes are needed to supportthe 1D array configuration. Such an arrangement is shown in FIG. 3, inwhich 219 switches are needed to control the array. in addition to thetwo switches per 2D-array element, the multiplexer requires oneadditional switch per column. The 2D array uses 100 coaxes whenacquiring a 3D image in the sparse 2D array configuration, and 19 ofthose coaxes when acquiring a 2D image in the full aperture 1Dconfiguration.

In the sparse 2D array mode, switches 2D0-2D8 are closed to connect thesparse 2D array elements 12 to coax cables C0-C9 (one element isconnected directly to coax C8). In the 1D mode, switches 2D0-2D8 areopen and switches 1D0-1D9 are closed to connect all of the elements ofthe first column 26 to coax cable C8. Switch 1D10 is also closed,connecting all of the elements of the second column 27 to coax cable C9.

FIGS. 4-7 illustrate another embodiment of the present invention inwhich different sets of elements are used for 3D imaging: a small, full2D aperture for transmit and a large, sparse 2D aperture for receive.FIG. 4 illustrates an approximately circular subset of a 19×19 2D array100 drawn with four types of shading as indicated to the right of thedrawing. The lightly shaded elements 102 are used for transmission inthe 2D array mode of operation for 3D imaging. The moderately shadedelements 104 are used for reception in the 2D array (3D imaging) mode.The darkly shaded elements 106 are used for both transmission andreception in the 2D array (3D imaging) mode. The unshaded elements 108are not used in the 2D array (three dimensional imaging) mode. All ofthe elements are used in the 1D array (two dimensional imaging mode) ofoperation. As a result, the elements which form the sparse 2D arrayconfiguration 110 of FIG. 5, which are elements 104 and 106 of FIG. 4,are used when the array receives echo signals during three dimensionalimaging as a sparse 2D array. The elements 112 used to transmit beamsfor the sparse 2D array mode are shown in FIG. 6, which correspond toelements 102 and 106 of FIG. 4. As the drawings illustrate, beams aretransmitted in three dimensions by the small, full 2D transmit apertureof FIG. 6, to generate echoes received by the sparse 2D receive apertureof FIG. 5.

In the 1D mode for two dimensional imaging, the elements of the columnsare connected together as shown in FIG. 7 to form the full 1D aperture114.

The 2D array used in FIGS. 4-7 can be a rectangular array as shown inthe previous drawings, or can be configured in a shape of more than foursides such as the octagonal shape of FIG. 4. These greater sidedpolygonal shapes lend themselves to use of the array transducer in arotating environment, such as the transducer for a multiplane TEE probeor rotating transthoracic probe as shown in U.S. Pat. No. 5,779,639,where they will fill a large percentage of the rotating aperture. Sincethe elements in the 1D array mode shown in FIG. 7 are of unequal lengthsand hence exhibit unequal sensitivities, the array will usually beoperated with apodization on either transmit or receive or both whenused in the 1D mode.

In the embodiments of FIGS. 4-7, a multiplexer is used to switch between2D transmit, 2D receive, and 1D modes of operation. A multiplexersubstantially the same as that described in the previous embodiment maybe used. The elements 108 not used in the 2D (three dimensional imaging)mode are grouped together in columns, with each column connected to acable through a single-pole single-throw switch as described above. Allof the elements 102, 104, 106 used in the 2D sparse array aperture havetwo switches, one to connect to a cable for 2D-array operation(transmit, receive, or both), and one to connect into a column for 1Doperation. The difference between this embodiment and the prior exampleis that the switches cannot be operated as single-pole double-throwswitches. This is because there will be situations where neither switchshould be closed: during 2D-array transmit operation those 2D receiveelements not in the transmit aperture would have neither switch closed;and during 2D-array receive operation those 2D transmit elements not inthe receive aperture would have neither switch closed.

In all of the cases described above it may be desirable to control theelectrical boundary condition on the 1D-only elements in 2D mode. Thiswill require only one switch per column.

Referring now to FIGS. 8a and 8 b, a transducer probe 120 constructed inaccordance with the principles of the present invention is shown. The 2Dtransducer array 10 has a dome-shaped lens 20 over thetransmitting/receiving side of the array to provide a greater acousticdelay in the center of the array than at the periphery of the array.This provides some of the delays required in the center of the array andreduces the longest delay demands on the beamformer. It also provides anadvantageous form factor for patient contact. Behind the array is anacoustic backing block 30 which damps acoustic emissions from the backof the array. The front of the array which faces the acoustic lens 20 iscovered by a metallized foil to provide a common electrical return forthe elements, and signal leads are connected to the back of the arrayelements. Alternatively the transducer elements may be operated in thek₃₁ mode, in which case all electrical connections can be made from theback of the array. Flex circuit interconnections extend through thebacking block 30 as described in U.S. Pat. No. 6,043,590 to provideelectrical signal connections between the elements of the array 10 andcomponents on a plurality of printed circuit boards 82. These componentsinclude multiplexer (MUX) switches 84 which are controlled toselectively interconnect elements of the 2D array to the cable assemblyas described herein. Suitable MUX switch packages are the HV202 SPST FETswitch packages available from Supertex, which contain both FET switchesand control logic to control the switches. The control logic and FETswitches of the MUX switches are connected by traces on the printedcircuit board to cable connection points 86 on the printed circuitboards, which can comprise connectors. Preferably these connectionpoints accommodate lead frames of the coaxial cables as described inU.S. Pat. No. 5,482,047.

The transducer stack and board subassembly shown in FIG. 8a, which mayhave one or more double-sided printed circuit boards with MUX switchpackages, are enclosed in a plastic case 80, one half of which is shownin FIG. 8b. In the rear of the case 80 is an indentation which enclosesthe strain relief of the cable. A protective lens of soft rubber or hardplastic may be formed over the acoustic lens 20 so that the protectivelens and case 80 provide an integrally sealed enclosure for the assemblyshown in FIG. 8a. The embodiment of these drawings accommodates arectilinear array transducer such as that shown in FIG. 1. Otherembodiments may use an array with more than four sides, such as thatshown in FIG. 4, which may be more suitable for certain cardiologyapplications where the probe needs to access the heart from between theribs. Such an embodiment may be more rounded and be of a different formfactor than that shown in FIGS. 8a and 8 b.

FIG. 9 illustrates in block diagram form an ultrasound system includinga transducer probe of the present invention. The transducer probeincludes a 2D array in a case 80 as described above. The transducerprobe is connected to the ultrasound system beamformer 202 by a cable 90and a probe connector 92. The beamformer 202 controls the times at whichsignals are applied to the elements of the 2D array which are used fortransmission, and delays and combines signals received from the elementsfor the transmission of steered and focused beams and for the dynamicfocusing and steering of received echo signals over a linear orvolumetric region. Operation of the beamformer is controlled by abeamformer controller 204 which controls the timing, steering,frequency, and focusing of transmitted and received beams in the normalmanner by data coupled to the beamformer 202 over a data bus 205. Inaddition, the beamformer controller 204 provides data over MUX controllines 207 which controls the setting of the switches that connectselected elements of the 2D array to each other and to the beamformer202 over the cable 90. As shown in FIGS. 4-7, the 2D array can havethree types of apertures: 2D transmit and 2D receive for threedimensional imaging, and 1D transmit/receive for two dimensionalimaging. Thus the cable includes signal leads and MUX control signalsfor the switches of the 2D array 10. The beamformer controller 204controls the beamformer in response to inputs from the user by way ofthe user interface 200, which may comprise a control panel or softkeyson the system display screen. For example, the user may command thesystem to acquire a three dimensional harmonic image using the sparse 2Darray switch settings and also to periodically acquire a two dimensionalDoppler flow image within the three dimensional volume using the 1Darray switch settings. The beamformer controller would then control thearray switches and beamformer to switch back and forth between thesedifferent modes in a time interleaved manner. The beamformed signals areB mode or Doppler processed by a signal processor 206 and formed into animage of the desired format and orientation by an image processor 208for display on an image display 210.

The MUX switches which control the imaging mode of the 2D array can belocated in several places, including within the handheld probe as shownin FIGS. 8a and 8 b, within the probe connector 92, or in the beamformer202. The beamformer usually will afford the most room for a switchprinted circuit board, and will also eliminate board coolingconsiderations from the scanhead design. Locating the MUX switches inthe probe connector 92 will enable the probe to be smaller and lighter,but at the expense of a larger cable needed to connect all of theelements of the 2D array to the connector. Locating the MUX switches inthe probe itself will reduce the cable size and eliminate cableimpedance effects from uncombined signals of the transducer elements.

FIGS. 10a-10 c illustrate a further embodiment of the present inventionby which the 2D array can be configured for imaging multiple twodimensional image planes. FIG. 10a shows a 2D array 300 in which thedark shaded elements 302 comprise the transducer elements which areoperated separately as a sparse 2D array for three dimensional imaging.For two dimensional imaging the columns of elements are connectedtogether by the MUX switches as shown by the vertical lines in thedrawing to form a 1D array having elevation and azimuth dimensionsindicated adjacent to the drawing. The 1D array uses both the elements302 used for the 2D array, as well as the unshaded elements 304 whichare not used for the sparse 2D array. While a full 1D array could beformed if desired, the drawing shows a sparse 1D array aperture which,as shown below, affords an ease in the switch matrix interconnection andsymmetry with the sparse 1D array aperture shown in FIG. 10b. The 1Darray shown in this drawing is formed by interconnecting transducerelements 306 in rows as indicated by the horizontal lines in thedrawings. The elements 306 are those which are spaced between theelements 302 and 304 in the full 2D array. Thus, two 1D arrays can beformed as shown in FIGS. 10a and 10 b with orthogonally oriented azimuthand elevation directions. As the drawings illustrate, both are 1D sparsearrays exhibiting the same spacing between elements and rows or columnsforming the 1D array elements.

FIG. 10c illustrates how the elements of the 2D array of FIGS. 10a and10 b can be interconnected for 1D and 2D array operation. The elementsrepresented by circles 310 are used as sparse 2D array elements forthree dimensional imaging and are separately controlled; each isconnected during three dimensional imaging to its own coax signalconductor of the probe cable. The elements shown as blocks 312, 314 mayall be grounded, connected to ground by an impedance, or left floatingduring three dimensional imaging. For two dimensional imaging as a 1Darray oriented as shown in FIG. 10a the columns of elements 312 arehardwired together as shown by lines 316 and each column is connected toa separate coax signal conductor of the probe cable, with each columnforming a 1D array element. In addition, the elements 310 in each columnare connected together to provide a 1D array element. These two sets ofcolumns provide a ED array that is fully sampled in azimuth but is 50%sparse in elevation. For two dimensional imaging as a 1D array orientedas shown an FIG. 10b the rows of elements 314 are hardwired together asshown by lines 318 and each row is connected to a separate coax signalconductor of the probe cable, with each row forming a 1D array element.

Since a transducer array of the present invention can alternate quicklybetween two and three dimensional image acquisition and can provide afuller, more sensitive 1D aperture for two dimensional imaging, it canperform spectral Doppler imaging without a change of transducer probes.FIG. 11 illustrates an imaging mode in which the probe is used toprovide a two dimensional image, a three dimensional image, an aspectral Doppler display simultaneously by a time interleavedacquisition sequence. At the left of display screen is a threedimensional image 400 which is acquired by the 2D array when operatingas a sparse 2D array. The three dimensional image provides an excellentsurvey tool by which the clinician can acquire a view of a volume oftissue and vasculature within the body. Since a volumetric region isbeing imaged, there is no problem with the anatomy being examined movinginto and out of the image plane; the anatomy can be kept in the centerof the volumetric region 400. In this case, coronary arteries 404 areimaged within the volumetric region. Additionally theorientation/location of the two dimensional image plane can bedelineated in the three dimensional volume even when two dimensionalimaging is not being used, as described in U.S. Pat. No. 5,353,354.

Periodically the scanning of the volumetric region in the 2D array modeis interrupted to acquire one or more scanlines of the planar image 402in the 1D array mode. The probe is moved until the desired anatomy, inthis example artery 406, is located in the plane of the image 402. Therest of the arterial branches 404 remain in the volumetric region oneither side of the image plane 402. To improve the ability to see thevasculature in the image plane 402 the tissue in the volumetric regionin front of the image plane, that is, between the viewer and the plane,can be made wholly or partially transparent as described in U.S. Pat.No. 5,720,291. In this example the image plane also contains a samplevolume cursor 410, which can be moved in the plane by the clinician topinpoint a location on the artery 406 at which a spectral Dopplermeasurement is made.

In the illustrated display mode the two dimensional image plane 402 isseparately displayed on the display screen as shown at the right of thedrawing, clearly showing the artery 406 of interest and the location ofthe sample volume 410. When the two dimensional image is separatelydisplayed it may be desirable only to designate the location of the twodimensional image plane in the three dimensional image 400 by anoutline, as described in U.S. Pat. No. 5,353,354. The two dimensionalimage 402 is preferably a colorflow image in which the bloodflow in theartery 406 is represented in color. For this display mode, the scanningof the volumetric region 400 would be periodically interrupted toacquire B mode lines of the two dimensional image 402 and Dopplerensembles for colorflow processing. Preferably the B mode and Dopplerscanning of the planar image 402, which is done by the 2D array whenswitched to operated as a 1D array, is done at a higher frame rate thanthe frame rate of the three dimensional display. Thus, within the Limerequired to scan the volumetric region once, more than one planarcolorflow image is acquired and displayed as shown at the upper rightside of the drawing.

The greater sensitivity of the 1D array enables a spectral Dopplerdisplay to be produced by either pulsed or continuous wave means asshown at 408 in the drawing. In this example the sample volume 401 isscanned at an even greater repetition rate than the two dimensional,image plane by operating the 2D array as a 1D array. The spectralDoppler sample volume transmit pulses, when operating in the pulsed waveDoppler mode, are time interleaved between the two dimensional imagingtransmit pulses, which are in turn time interleaved between the threedimensional imaging pulses. The echo information acquired from thesample volume is Doppler processed and displayed as a spectral displayas shown at 408, with the bloodflow velocity within the sample volumebeing shown as a function of time. Thus, a probe of the presentinvention can be used as a volumetric survey tool, a more sensitive twodimensional imaging probe, and a spectral Doppler probe for quantifiedmeasurements either successively or simultaneously without changingprobes.

Numerous variations which take advantage of the capabilities of a probeof the present invention are also possible. For example, the display 408in FIG. 11 can be a scrolling display of M-mode lines rather thanspectral Doppler lines. In such case the sample volume 410 would bereplaced by a user adjustable M-line to denote the line along which theM-mode display is to be produced. Such a display could for instance showthe heart in three dimensions, a plane of the heart in two dimensions,and an M-mode display of the pulsatile motion of the heart wall alongthe M-line. The M-mode could be a B mode display, or could use Dopplerinformation to produce a tissue Doppler or colorflow Doppler M-modedisplay. The M-lines of the M-mode display are produced at a rate whichis greater than the frame rate of the two dimensional display and thethree dimensional frame rate of display. The greater frame rate,resolution, and sensitivity of the two dimensional image lend themselvesto contrast imaging, in particular perfusion imaging of the myocardium,as well as other types of quantified measures besides Dopplermeasurements. The greater sensitivity of the 1D array configuration alsomakes possible the imaging of a two dimensional plane with the 1D arrayconfiguration operating in the harmonic mode while the 2D arrayconfiguration is operated in the fundamental mode. Although a sparse 2Darray may not exhibit sufficient sensitivity for tissue harmonic imagingwhen performing three dimensional scanning, this limitation is overcomeby use of a fully populated 1D array for the two dimensional image,where greater sensitivity for tissue harmonic imaging is afforded.

FIG. 12 illustrates a 2D array 300′ when operated to provide two planarimages within a volumetric region as discussed above with reference toFIGS. 10a-10 c. In this case the array is operated as a 2D array to scana volumetric region 500. When switched to form orthogonally oriented 1Darrays, the array can scan either two dimensional plane 502 or twodimensional plane 504. A desirable format for this mode of imaging wouldbe to display a three dimensional image of the volumetric region 500with an adjacent planar image 502 as shown in FIG. 11 by threedimensional image 400 and planar image 402, and an additional adjacentplanar image 504. As the probe is moved in relation to the body, anatomywould move into and out of the volumetric region 500, and more quicklyinto and out of the two image planes 502 and 504. The clinician can thusscan the body in three dimensions and in two image planes in real time.As mentioned above, the array can be operated in the fundamental modewhen operated as a 2D array, and in the harmonic mode for tissueharmonic imaging of the two image planes when operated as a 1D array totake advantage of the greater sensitivity of the 1D arrays. When arrayshaving a grid pattern other than a square one are employed, such as thehexagonal 2D array described in U.S. Patent [application Ser. No.09/488,583 filed Jan. 21, 2000], the image planes may be oriented onplanes aligned with the grid pattern. A hexagonal 2D array may producetwo or three image planes separated by 60 degrees rather than two imageplanes separated by 90 degrees as shown in FIG. 12.

A transducer array of the present invention can be used in all of theusual diagnostic ultrasound modes, including in different harmonic modesand with or without the use of contrast agents. The array can be usedfor volumetric panoramic imaging, where the array is operated as a 2Darray as it is moved along the body to acquire an extended field of viewimage of a volumetric region. References to three dimensional imagingand volumetric scanning also include volumetric acquisition, where thedata of a volumetric region is acquired but only selected planes withinthe volume are displayed in detail.

What is claimed is:
 1. An ultrasonic diagnostic imaging scanheadcomprising: a scanhead case having an acoustic window; a two dimensionalarray transducer having a plurality of columns and rows of transducerelements located in the case and directed for scanning through theacoustic window; a substrate, located in the case, and containing aplurality of single pole, single throw switches coupled to a pluralityof the elements of columns of the array transducer which selectivelyconnect the elements of the columns of the array for operation aselements of a 1D array, and selectively connect a plurality of elementsof ones of the columns for individual operation as elements of a 2Darray; and a cable coupled to the switches which connects the scanheadto an ultrasound system.
 2. The ultrasonic diagnostic imaging scanheadof claim 1, wherein the substrate comprises a printed circuit board. 3.The ultrasonic diagnostic imaging scanhead of claim 1, wherein theswitches act in response to signals from an ultrasound system connectedby means of the cable to selectively connect elements of the twodimensional array for operation as a 2D or a 1D array.
 4. The ultrasonicdiagnostic imaging scanhead of claim 3, wherein the switches act toselectively connect elements of the two dimensional array for operationas a sparse 2D array or a 1D array.
 5. The ultrasonic diagnostic imagingscanhead of claim 4, wherein the switches act to selectively connectelements of the two dimensional array for operation as a sparse 2D arrayor a full aperture 1D array.
 6. The ultrasonic diagnostic imagingscanhead of claim 2, further comprising a cable connector, located onthe printed circuit board, for connecting the cable to circuitry on theprinted circuit board.
 7. The ultrasonic diagnostic imaging scanhead ofclaim 1, wherein the cable includes at least one conductor for couplingswitch control signals from the ultrasound system to the switches, and aplurality of signal conductors for coupling ultrasound signals fromelements of the transducer array to the ultrasound system.
 8. Theultrasonic diagnostic imaging scanhead of claim 1, wherein the switchesact to selectively connect elements of the two dimensional array foroperation as a sparse 2D receiving array or a full aperture 2Dtransmitting array.
 9. The ultrasonic diagnostic imaging scanhead ofclaim 1, wherein all of the switches which selectively connect theelements of the array for 1D or 2D operation comprise single pole,single throw switches.
 10. A two dimensional array of acousticallyseparate ultrasonic transducer elements, individual ones of which arearrayed in two dimensions and a plurality of switches, coupled toelements of the array, which selectively couple the elements foroperation as a 1D array having an azimuth dimension in a first directionand an orthogonal elevation dimension, and as a 1D array having anazimuth dimension in a second direction and an orthogonal elevationdimension.
 11. The two dimensional array of ultrasonic transducerelements of claim 10, wherein the 1D arrays are sparse arrays.
 12. Thetwo dimensional array of ultrasonic transducer elements of claim 11,wherein alternate elements on alternate rows of elements of the arrayare interconnected to operate the array as a 1D array having the azimuthdimension in the first direction, and alternate elements on alternatecolumns of elements of the array are interconnected to operate the arrayas a 1D array having the azimuth dimension in the second direction. 13.The two dimensional array of ultrasonic transducer elements of claim 10,wherein individual elements of the array are selectively operable as a2D array.
 14. The two dimensional array of ultrasonic transducerelements of claim 13, wherein individual elements of the array areselectively operable as a sparse 2D array.
 15. A two dimensional arrayof ultrasonic transducer elements, individual ones of which are arrayedin two dimensions and selectively operable as a 2D array to scan a threedimensional volume, or as two or more 1D arrays to scan two or moreimage planes intersecting the three dimensional volume.
 16. The twodimensional array of ultrasonic transducer elements of claim 15, whereinthe two dimensional array exhibits a given grid pattern, and wherein theimage planes exhibit a relative alignment which is a function of thegrid pattern.
 17. The two dimensional array of ultrasonic transducerelements of claim 16, wherein the grid pattern is a hexagonal gridpattern, and wherein the image planes exhibit a relative alignment ofsixty degrees.